The famous, or perhaps more properly, infamous Manhattan Project achieved its declared objective in the explosion of the first atomic bomb near Alamogordo, New Mexico, on July 16th, 1945. Many years later the leader of the Los Alamos team, Robert Oppenheimer, recalled: "A few people laughed, a few people cried. Most people remained silent. I remembered a line from Bhagavad Gita: `I am become Death, the destroyer of worlds', and I suppose we all thought that, one way or another."
No time was lost in putting this destroyer of worlds about its lethal business. Less than three weeks later - and 53 years ago today, on August 6th, 1945 - the atomic bomb was dropped on the Japanese city of Hiroshima, beginning an era during which the threat of unimaginable destruction has hung like a sword of Damocles over all the human race.
In the intervening years meteorologists have from time to time examined the implications of a large-scale nuclear war for their particular sphere of interest. At first they came to very frightening conclusions: it appeared that the initial destruction was not the only horror to be faced, but that there would also be a very dramatic change in the world's climate.
It was reckoned there would be great fires spread over many thousands of square miles, and that these would generate great quantities of sooty smoke to form a dense pall around the middle latitudes of the northern hemisphere.
For several weeks, it was predicted, as little as 5 per cent of the sun's radiant energy would penetrate the layer of smoke, and the resulting darkness would only slowly give way to gloomy, twilight conditions. The reduction in solar energy was calculated to bring a drop in temperature of up to 35 C, and since this fall was comparable to that from summer to winter in the centre of a large continent, the phrase nuclear winter was coined.
Later studies, however, have been less apocalyptic. Instead of assuming that smoke would be spread evenly over the whole globe, more recent researchers have acted on the realistic assumption that the obscuration would be patchy, some areas overcast, and others largely unaffected for considerable lengths of time. They also took into account the temporarily-enhanced "greenhouse effect" of the pollutants, which would decrease the rate at which the temperature might fall.
These more sophisticated models predict a temporary drop in temperature of about 10C in the northern hemisphere, a scenario which scientists sometimes refer to as a "nuclear autumn". The reassuring inference is that from a meteorological viewpoint nuclear war would be only slightly catastrophic.